Mohammad T. Rayhani

Hydraulic performance of Compacted Clay Liners (CCLs) under combined temperature and leachate exposures

Experimental investigations were carried out to investigate the effect of thermo-chemical exposures on the hydraulic performance of Compacted Clay Liners (CCLs) in landfills. Hydraulic conductivity of most CCL specimens was increased by two to three times their initial values when exposed to 55 °C for 75 days. CCL specimens also experienced increases in their hydraulic conductivities when exposed to leachate at room temperature. This behaviour could be due to the decrease in viscosity when the permeant was changed from tap water to leachate. However, as the leachate exposure time exceeded the first 15 days, hydraulic conductivity readings decreased to as much as one order of magnitude after 75 days of leachate permeation at room temperature. The gradual decrease in the CCLs hydraulic conductivities was most likely due to chemical precipitation and clogging of pore voids within the soils which seemed to reduce the effective pore volume. The rate of hydraulic conductivity reduction due to leachate permeation was slower at higher temperatures, which was attributed to the lower permeant viscosity and lower clogging occurrence. The observed hydraulic behaviours were correlated to the physical, mineral, and chemical properties of the CCLs and described below.

Seismic response of sands in centrifuge tests

Seismic site response of sandy soils and seismic soil-structure interaction are investigated using an electro- hydraulic earthquake simulator mounted on a centrifuge container at an 80g field. The results of testing uniform and lay- ered loose to medium-dense sand models subjected to 13 simulated earthquakes on the centrifuge are presented. The variation of shear modulus and damping ratio with shear strain amplitude and confining pressure was evaluated and their effects on site response were assessed. The evaluated shear modulus and damping ratio agreed reasonably with laboratory tests and empirical relationships. Site response analysis using the measured shear wave velocity and estimated modulus re- duction and damping ratio as input parameters produced good agreement with the measured site response. The effect of soil-structure interaction for structures situated on dry sand is also investigated. These tests have revealed many important insights with regard to the characteristics of seismic site response and seismic soil-structure behaviour. The tests showed that the seismic response of soil deposits, input motions, and overall behaviour of the structure are affected by soil stratifi- cation. The results showed that the seismic kinematic soil-structure interaction is not very significant for structures situated on loose sand.

Characterization of Glyben for Seismic Applications

Glyben is an artificial clay prepared by mixing sodium bentonite powder and glycerin. It is used for lab tests and scale modeling for geotechnical applications. The mechanical properties of glyben depend on the bentonite and glycerin mix proportions. In this research, the shear strength, dynamic shear modulus, damping ratio, and Poisson’s ratio were evaluated for glyben samples prepared with different glycerin/bentonite ratios. Vane shear tests, T-bar tests, hammer tests, and resonant column tests were also conducted on glyben specimens and the shear strength and dynamic properties were evaluated considering a wide range of strain values and confining pressures. The measured glyben properties were compared with properties of natural cohesive soils to verify the range of applicability of glyben as a test bed material. It was found that glyben has the same range of strength and dynamic properties as soft to medium stiff clay. The trend of variation of the shear modulus and damping ratios of glyben is similar to that of natural clays. It is noted, however, that the damping ratio of glyben is higher than that of natural clays for shear strains below 0.01%. It was concluded that glyben can reasonably model the nonlinear behavior of natural soil under strong dynamic excitation.

Hydration of geosynthetic clay liners from clay subsoil under simulated field conditions

Use of Geosynthetic Clay Liners (GCLs) in landfill barrier design has been the focus of recent studies investigating their ability to prevent contaminant transport to groundwater. In this paper, the hydration of two GCL products placed in contact with clay subsoils at different initial moisture contents is described under both isothermal conditions at room temperature, and daily thermal cycles. The rate of hydration of the GCL and its final equilibrium moisture content were significantly influenced by the amount of moisture made available to it through the subsoil. The two types of GCLs were also found to exhibit different hydration behaviors under similar experimental conditions. The study revealed that GCLs undergoing daily thermal cycles absorbed much less moisture over time than the GCLs kept at constant room temperature (ratio 1:4). In comparison with other types of subsoils, the final equilibrium moisture content attained by the GCL from clay subsoil was significantly less than that for sand subsoil.

Effect of temperature on hydration of geosynthetic clay liners in landfills

Geosynthetic clay liners (GCLs) have gained popularity as a barrier system in modern landfill construction. As such, it is depended upon to provide a level of impermeability to prevent the escape of contaminants into the surrounding soil and groundwater. It has been proven that a GCL’s hydraulic conductivity is closely related to its moisture content. GCLs are known to absorb moisture from the underlying soil after installation. In a landfill, temperatures near the liner can reach upwards of 55ºC. The effect of these elevated temperatures on the hydration process of the GCL was determined for two types of GCL over two types of subsoil: sand and clay. It was found that elevated temperatures prevented the GCL from reaching moisture content levels that would be acceptable in a real-life scenario. Temperatures in landfills could be expected to cause a GCL to reach a moisture equilibrium at roughly 16% gravimetric moisture content, where GCL at room temperature would reach higher than 100% gravimetric moisture content. The significant difference in moisture equilibrium of GCLs at different temperatures may suggest that the heat naturally produced in landfills could negatively affect the liner’s hydraulic performance. The importance of allowing a GCL to properly hydrate before heat exposure must be better understood in order to minimize the potential negative effect of a landfill on our environment and our livelihood. This study also confirmed that the hydration potential of GCL depends on the method of GCL manufacture and the subsoil characteristics.

Effect of explosive cratering on embankment dams

The efficient management and protection of critical infrastructure such as dams is relevant to safety of the population of low-lying downstream communities. Ramifications of dam breach on these communities would be severe and include loss of electricity, flooding, injury and fatality. The economic losses can be enormous depending on the size of the dam and level of emergency preparedness of the community. As acts of terror continue to increase globally, dams appear to be attractive targets due to the capacity to adversely impact downstream communities and to attract media attention. Embankment dams are more susceptible to cratering and, in turn, overtopping and erosion of the dam crest. This paper investigates the effects of explosions on embankment dams by using a high-fidelity physics-based numerical analysis software program – LS-DYNA. The impacts of explosive size, reservoir level and soil density were examined while measuring the dimensions of the resulting crater. The investigation showed that an increase in explosive size led to an increase in crater diameters as well as the depth. In considering the reservoir level, the reservoir was considered at maximum capacity, at mid-capacity and embankment without a reservoir. The results showed that the crater dimensions were larger at maximum capacity and lowest when there was no water in reservoir. At a given soil density, when the dam fill materials are saturated, the crater dimensions are larger in terms of diameters and depths as compared to when fill materials are not saturated.

Adfreeze Strength and Creep Behavior of Pile Foundations in Warming Permafrost

An experimental investigation was carried out to evaluate the thermal exposure effect on load carrying capacity and creep behavior of steel piles embedded in ice-poor frozen soils using steel-soil interface tests. The interface testing was conducted in a walk-in cold room to enable testing at various temperatures below the freezing point. A series of stress-displacement curves were established at different temperatures and under various normal stresses. The results showed a significant reduction in adfreeze strength of the pile-soil interface as the exposure surface temperature increased. The interface strength decreased approximately 300% when the exposure temperature increased from −1.5 °C to 0 °C. Such condition may be witnessed in warm permafrost that experience temperature ranging from −3 °C to 0 °C. The shear stress–strain curves showed a brittle behavior followed by significant loss of bearing capacity. Pile creep rate in ice-poor soils increased by about 60% when the interface was exposed to warming from −10 °C to −5 °C and showed tertiary creep when reaching −4 °C.

Comprehensive nonlinear seismic ground response analysis of sensitive clays: case study—Leda clay in Ottawa, Canada

A series of time domain nonlinear and frequency domain equivalent-linear ground response analysis was conducted for a representative site in Ottawa, Canada. The objective is to provide insight into the performance of different site response analysis approaches in predicting site amplification factors for the soft soil deposit over a wide range of shear strain. The surficial geology of the site is predominantly composed of the sensitive Leda Clay typical of this region in eastern Canada. A combination of results and observations from monotonic and cyclic laboratory tests, as well as field geophysical experiments, was used to calibrate the dynamic properties of the Leda clay, more specifically, the variation of the clay’s shear stiffness (Gmax) with the in situ stress state (

Geosynthetic clay liners shrinkage under simulated daily thermal cycles

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